1. Field of the Invention
The present invention relates to dynamic information storage and retrieval, particularly to disk players, and more particularly to suppression of resonance, or wobbling, due to the rotation of the disk.
2. Description of the Related Art
In general, a disk player records and/or reads information onto and/or from a recording medium such as a compact disk (CD), a CD-ROM, a digital versatile disk (DVD), and a DVD-ROM. Due to the sensitivity of the reading/recording process to vibration, the disk player must protect the disk and optical pickup from external impacts and internal vibrations.
A typical disk player includes a deck base hinge-coupled to a housing to be capable of rotating vertically, a deck plate coupled to the deck base, a spindle motor installed at the deck plate for providing a rotational force to a disk, a turntable coupled to a rotational shaft of the spindle motor for accommodating the disk, a damper installed on the inner surface of the upper portion of the housing to face the turntable for securing the disk placed on the turntable, and an optical pickup coupled to the deck plate to be capable of moving across the disk for performing recording and reproduction operations. The disk player includes dampening members disposed between the deck base and the deck plate to prevent external vibrations transferred through the deck base from being transferred directly to the deck plate, the spindle motor and the optical pickup. The dampening member is formed of a material such as soft rubber or polyurethane which can absorb external impacts.
The disk player adopting the dampening member as above can effectively protect the driving of the disk and the optical pickup from external impacts. However, a method of dampening internal vibrations generated by the rotation of the spindle motor due to an eccentric center of gravity of the disk is not provided for. Here, the eccentric center of gravity of the disk is caused by a discrepancy between the rotational center of the disk and the center of gravity of the disk due to errors in the manufacturing process of the disk. Thus, the rotational shaft of the spindle motor wobbles, or revolves, as it rotates.
Such wobbling of the rotational shaft of the spindle motor does not affect low-speed disk players such as a 1.times. or 2.times. disk players. However, in the case of high-speed disk players such as a 6.times.-40.times. disk players, the effects of wobbling of the spindle motor become serious, making recording/reproducing of information difficult. To overcome the above problems, in a conventional high-speed disk player, the mass of the deck plate where the spindle motor is installed is increased or the rigidity of the dampening member is increased to reduce movements of the deck plate due to the eccentric center of gravity of the disk.
However, not only is an inappropriately increased mass of the deck plate required for high speed rotation, but also the cost of the product increases and miniaturization of the product is hindered. Also, when the rigidity of the dampening member is increased, it is not possible to effectively dampen external impacts or vibrations.
Taking the above problems into consideration, U.S. patent application Ser. No. 08/947,895 filed on Oct. 9, 1997 by the present applicant discloses a disk player adopting a self-compensating dynamic balancer. The disclosed apparatuses use the relationship between an eccentric center of gravity position of a disk, the position of a rotation shaft and the center of rotation respectively according to different rotation speeds of the disk.
When the rate of orbital rotation of the spindle motor is less than or equal to the natural frequency of the deck plate, the natural frequency is determined by the elastic modulus of the dampening member and the mass of the deck plate and other elements to be installed on the deck plate, and represents the rate of vibration in a horizontal direction, i.e., in a direction parallel to the plane of the disk. When an eccentric center of gravity exists at a position spaced apart by a predetermined distance from the ideal rotation center of the disk, the ideal rotation center of the disk rotates around a center. In this case, the respective positions of the eccentric center of gravity and the revolution center of the disk are located opposite each other with respect to each of the ideal rotation center positions of the disk.
When the rate of revolution of the spindle motor is near the natural frequency of the deck plate, the revolution center is located in a direction perpendicular to that of the respective eccentric center of gravity positions with respect to the ideal rotation center positions. When the rate of revolution of the spindle motor is greater than the natural frequency of the deck plate, which corresponds to the normal rotation speed of a disk allowing information to be recorded onto or read from the disk, the revolution center is located in the same direction as the respective eccentric center of gravity positions with respect to the ideal rotation center positions.
As described above, in order to use the relationship between the center of revolution and the eccentric center of gravity of the disk, the self-compensating dynamic balancer is adopted to a rotating body such as the turntable, a rotor of the spindle motor, a rotation shaft of the spindle motor, and the clamper. Thus, the compensated mass of the self-compensating dynamic balancer and the eccentric mass are located in opposite directions with respect to the rotation shaft of the rotating body so that the internal vibrations of a disk player are effectively reduced. As shown in the above, when the self-compensating dynamic balancer is adopted, external impacts can be dampened by adopting dampening members exhibiting a relatively weak rigidity. However, the above balancer may lose balancing capability since a contact area with the balls forming the compensated mass is large.